1. Field of Invention
The present invention relates to optical networks, such as MAN (metropolitan area networks), SAN (storage area networks), access optical networks, and enterprise networks. The invention further relates to optical networks and optical fabric-switches. In particular, the invention relates to various implementations of a reservation based Media Access Control (MAC) network/switch fabric.
2. Description of Related Art
Fiber-optic infrastructure is a vital part of today's rapidly changing worldwide networks. The drive for interconnectivity as well as the exponential growth in data traffic as a result of new applications leads to the adoption of new optical solutions. Carriers and service providers are looking to increase their revenue by deliver new services such as storage area networks (SAN) and IP based services to customers. Similar to that, enterprises are looking to enhance their enterprise area networks to supply the bandwidth demands to the increasing needs. Technologies are needed that can leverage existing networks as well as increase the economic viability of new network applications. Recent advances in optical technologies (such as wavelength division multiplexing, tunable lasers, tunable receivers, and high-speed optical/electronic components) have led to new developments in the optical networks area.
The traditional optical networks were mainly used in the long-haul area networks; however, new optical networks are being introduced in the regional, metropolitan, access and enterprise area networks. The new optical networks, whether they are built as an all-optical network or as a central network with optical switch fabrics, are facing different demands. Optical networks require sustaining high bandwidth while maintaining mesh connectivity and supporting multiple services and multiple classes of service. For example, metropolitan area networks (MANs) can transport voice traffic, SAN traffic and IP traffic. Voice traffic demands low bandwidth with guaranteed latency, while IP traffic is burst traffic and requires large bandwidth. Switch fabrics, which are the core of the network switches/routers, are required to support low latency, while sustaining high bandwidth and many ports.
All optical networks or switch fabrics are basically packet-switched; in other words, routing of packets from a source optical element to a destination optical element is done optically, without the need for optical-electrical conversions outside the source and destination optical elements.
A sub-group of the all-optical networks/fabric-switches is the all-optical multi-ring. All-optical multi-ring networks/fabric-switches are based on a fiber ring topology, in which the fiber-ring is a shared optical medium. The network/fabric-switch nodes (optical elements), located around the fiber-ring, are equipped with either a tunable optical receiver or with a tunable transmitter or with a tunable receiver and transmitter. An addition sub-group of the all-optical networks/fabric-switches is the all-optical star coupled. All-optical star coupled networks/fabric-switches are based on an optical star coupler to which all the optical elements are connected. Nodes, connected to the coupler, are equipped with either tunable optical receiver or with tunable transmitter or with tunable receiver and transmitter.
Many such prior art networks are referred to as synchronous and slotted networks, where the fiber ring is essentially divided into a plurality of time slots, with the time slots rotating uni-directionally around the ring. In some cases, two rings can be used with each node transmitting the same data on each ring, but in opposite directions. Nodes can transmit a packet only within the boundaries of a time slot. The length of the time slot is typically fixed. Scheduling of packets is typically performed through the scheduling of wavelengths and time slots. In order to avoid collisions in time slots, only one node can transmit on each wavelength. Once a time slot has a packet at a particular wavelength, no other node can transmit in that time slot at that wavelength thereby freeing the wavelengths at that time slot.
The MMR and the SRR works (By Marco Ajmone Marsan, Andrea Bianco, Emilio Leonardi, A. Morabito, and Fabio Neri) deal with a slotted all-optical multi-ring topology. The MAC algorithm presented in these works is based on carrier-sense ability of each node and a fairness algorithm to prevent nodes starvation. The carrier-sense feature gives the network the ability to adapt transmission resources according to the traffic. Thus, the network bandwidth can be used more optimally. However, this approach has also a drawback that the algorithm lacks the ability to reserve bandwidth; consequently, the network does not support constant bit-rate traffic.
One version of this issue was being dealt in the SR3 algorithm developed by the same authors (“SR3: A Bandwidth-Reservation MAC Protocol for Multimedia Applications over All-Optical WDM Multi-Rings”, Marco Ajmone Marsan, Andrea Bianco, Emilio Leonardi, A. Morabito, Fabio Neri). The SR3 algorithm is also based on the carrier-sense idea with additional capability of reserving bandwidth between two nodes. The reserve bandwidth between from source node to a specific destination node can be up to 1/N of the bandwidth (N is the number of nodes). Although the SR3 algorithm supports reservation and thus supports constant bit-rate traffic, the reservation limitation, which increases as the number of the nodes increases, limits the bandwidth that can be allocated to constant bit-rate traffic. Furthermore the carrier-sense approach requires a fairness algorithm in order to avoid node starvations. The fairness algorithm base on the SAT token can cause large delays. The delays created by the fairness algorithm causes that a fairness-based networks cannot transport delay sensitive traffic, such as voice/video traffic. In order to improve the fairness algorithm and minimize the delays an improved fairness algorithm was proposed by I. Cidon, L. Georgiadis, R. Guerin, and Y. Shavitt (“Improved Fairness Algorithm for Rings with Spatial Reuse”).